As two senior Khmer Rouge leaders appear in court, we ask if their trial is mere symbolism or if justice will be served.

Two of the most senior surviving members of the Khmer Rouge regime, which terrorised the country for years, have appeared in court; and they have denied any guilt.

Charged with genocide and crimes against humanity, Nuon Chea and Khieu Samphan are accused of planning the deaths of two million Cambodians. They face life imprisonment if found guilty.

It took almost three decades to bring the senior leaders of the Khmer Rouge regime to trial, to justice. From the Cambodian perspective, it is significant to find justice and truth and consolation for the Cambodian society. They need to face the past in order to heal the present. So the Khmer Rouge tribunal is part of this justice for Cambodian society.

Chheang Vannarith, a senior fellow at the Cambodian Institute for Co-operation and Peace

Chea was the second in command during the Khmer Rouge's rule in the 1970s, and Samphan was the head of state when the regime was in power.

Both presented their final defence on Thursday as the two-year trial comes to an end, and both distanced themselves from the allegations against them.

Chea denied all charges against him during his final defence to the court, defending his actions and saying he did not order Khmer Rouge cadres to kill. But he did accept "moral responsibility" for the deaths of millions of Cambodians.

The two will be sentenced next year.

The Khmer Rouge started out as a communist-inspired guerrilla movement in the 1960s.

Led by Pol Pot, the rebels moved out of Cambodia's northeastern jungles, and eventually took power. They ruled Cambodia from 1975 to 1979.

When they seized the capital, Phnom Penh, the Khmer Rouge marched more than two million people to labour camps in the countryside - one of the largest forced migrations in modern history.

Businessmen, intellectuals, Buddhists and foreigners were all 'purged' under the communist regime.

In total, some two million people - up to a quarter of the population - were killed through a combination of executions, starvation and overwork.

In recent years, the International Criminal Court has pursued a number of global leaders accused of using violence against their own people.

The former president of Serbia, Slobodan Milosevic, was indicted for crimes against humanity in 1999. But he died in 2006 before his trial came to an end.

Last year, former Liberian President Charles Taylor was found guilty of aiding and abetting war crimes and crimes against humanity. He was sentenced to 50 years in prison.

Others to be indicted but never convicted include former Libyan leader Muammar Gaddafi, who died in the 2011 revolution, and Sudanese President Omar al-Bashir, who is facing several counts of crimes against humanity, genocide and war crimes.

So, to what extent are these court proceedings symbolic, and more about demonstrating accountability than exercising justice?

Will justice be served for those who died in killing fields of Cambodia? And will this trial deter other rulers and regimes from violating human rights?

To discuss this, Inside Story, with presenter Mike Hanna, is joined by guests: Nicholas Koumjian, a prosecutor for the Extraordinary Chambers in the Courts of Cambodia (ECCC), which receives assistance from the United Nations; Chheang Vannarith, a senior fellow at the Cambodian Institute for Co-operation and Peace; and David Tolbert, the president of the International Center for Transitional Justice.

"I do think it was important that these senior leaders were brought to justice, but it is clearly an incomplete process and a good bit more needs to be done on the criminal prosecution front, and I don't think any of us are optimistic that that is going to happen .... Getting the truth out is still a very difficult task and it is clear that there are parts of the government that don't want to see the complete truth out. So I think the tribunal has done some good, but much of the potential has not been realised and, unfortunately, does not look to be realised."

David Tolbert, the president of the International Center for Transitional Justice